The invention specially relates to preparation of cucurbitadienol and application of cucurbitadienol as an STAT3 and ERK signaling pathway target drug to medicines used for treating tumors, belonging to the field of tumor drugs. A preparation method for cucurbitadienol comprises the following steps: successively carrying out pretreatment, extraction, separation and purification; then rapidly and highly-efficiently extracting crude cucurbitadienol extract by using a supercritical method; and carrying out high-efficiency liquid-phase preparation to obtain high-purity cucurbitadienol. In application to medicines used for treating tumors, cucurbitadienol uses an STAT3 signaling pathway and/or an ERK signaling pathway as a drug target. Through selective inhibition of the STAT3 and ERK signaling pathways, cucurbitadienol induces cycle arrest of cancer cells and promotes apoptosis of cancer cells so as to inhibit propagation of cancer cells.